This invention relates to positive-displacement fluid machines which may be used as motors, pumps, or compressors, of the type made up by two units defining between them at least one groove of constant section, and movable one relative to the other in the direction of said groove, at least one piston integral with one of said two units, which piston has a working section conjugate with that of said groove and is engaged in a fluid-tight manner in the groove, movable partitions in the other of said two units in such manner as to bring about selectively in said groove, to the fluid-work chambers, means for putting said chambers into communication with an inlet orifice and an outlet orifice, and cams for controlling said movable partition, said cams being unitary with the unit which carries the piston or pistons and co-operating with the ends of said partition in order to impress upon the latter a to-and-fro movement synchronized with the relative movement of said two units.
In known machines of this type, the displacements of the movable partitions are mechanically ensured by the cams, so that the movements of said cams, which must be abrupt, lead to a certain amount of wear of the mechanism.